Physicists create optical phenomenon inspired by the quantum Hall and spin Hall effects

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Researchers at the Würzburg site of the Cluster of Excellence ctd.qmat have succeeded in transferring the topological quantum Hall and spin Hall effects to a hybrid light-matter system by harnessing targeted material design. The team led by Professor Sebastian Klembt generated this optical quantum phenomenon by using polaritons—hybrid light-matter particles. This advance paves the way for optical information processing. The results have been published in Nature Communications.

From the quantum Hall and quantum spin Hall effects to light

Back in 1980, Nobel laureate Klaus von Klitzing, then working in Würzburg, first demonstrated topological charge transport with the quantum Hall effect.

In 2006, Professor Laurens Molenkamp at JMU Würzburg provided the world's first experimental evidence of the quantum spin Hall effect as an intrinsic property of a topological insulator. Both phenomena protect electrons from scattering.

Now, Sebastian Klembt from the Chair of Applied Physics, a Principal Investigator at the Würzburg-Dresden Cluster of Excellence ctd.qmat—Complexity, Topology and Dynamics in Quantum Matter and recently appointed Professor of Experimental Physics I at JMU Würzburg, has transferred these effects to a hybrid quantum material together with an international team.

To achieve this, the researchers used polaritons—a hybrid of light (photons) and matter (excitons). These form in "micropillars"—tiny semiconductor structures in which light and matter interact strongly.

The experiments were carried out at the Chair of Applied Physics at JMU Würzburg led by Simon Widmann. The theoretical framework was developed in collaboration with Ronny Thomale—also a Principal Investigator at ctd.qmat and Professor of Theoretical Physics I—as well as researchers from Nanyang Technological University, Singapore.

The breakthrough: Pseudospin through targeted material design

"Our microstructures are much smaller than the diameter of a human hair. We engineered them in the cleanroom to give our laser light unique properties. The topological light transport we demonstrated—and the underlying effect—open up new possibilities for topological polariton lasers and optical information processing," explains Sebastian Klembt.

The Würzburg researchers engineered gallium arsenide (GaAs) into a chain of elliptically shaped micropillars. When laser light hits the sample, photons interact with excitons to form hybrid polaritons. Mirror layers confine these particles within the micropillars, where they behave like electrons in topological transport.

"The elliptical shape of the micropillars and the angles at which they are coupled generate what is known as an artificial gauge field. Much like a magnetic field acting on electrons, this gauge field determines the behavior of our polaritons," Klembt adds.

In this hybrid material system, the geometry causes light to become either left- or right-circularly polarized—meaning the electric field rotates clockwise or counterclockwise. These two polarizations propagate along opposite paths, forming an optical analog of the quantum spin Hall effect. "The circular polarization of light acts as a pseudospin," says Klembt.

The findings open up new possibilities for applications such as topological polariton lasers, spin-based transistors, and optical information processing. In this context, the polarization of light can also serve as an information carrier.

Publication details

Simon Widmann et al, Artificial gauge fields and dimensions in a polariton hofstadter ladder, Nature Communications (2026). DOI: 10.1038/s41467-026-68530-0

Journal information: Nature Communications

Key concepts

Optics & lasersQuasiparticles & collective excitationsTopological phases of matterTransport phenomena

Provided by University of Würzburg